Simulating the integrated summertime Delta(CO2)-C-14 signature from anthropogenic emissions over Western Europe

Abstract. Radiocarbon dioxide ( 14 CO 2 , reported in Δ 14 CO 2 ) can be used to determine the fossil fuel CO 2 addition to the atmosphere, since fossil fuel CO 2 no longer contains any 14 C. After the release of CO 2 at the source, atmospheric transport causes dilution of strong local signals into the background and detectable gradients of Δ 14 CO 2 only remain in areas with high fossil fuel emissions. This fossil fuel signal can moreover be partially masked by the enriching effect that anthropogenic emissions of 14 CO 2 from the nuclear industry have on the atmospheric Δ 14 CO 2 signature. In this paper, we investigate the regional gradients in 14 CO 2 over the European continent and quantify the effect of the emissions from nuclear industry. We simulate the emissions and transport of fossil fuel CO 2 and nuclear 14 CO 2 for Western Europe using the Weather Research and Forecast model (WRF-Chem) for a period covering 6 summer months in 2008. We evaluate the expected CO 2 gradients and the resulting Δ 14 CO 2 in simulated integrated air samples over this period, as well as in simulated plant samples. We find that the average gradients of fossil fuel CO 2 in the lower 1200 m of the atmosphere are close to 15 ppm at a 12 km × 12 km horizontal resolution. The nuclear influence on Δ 14 CO 2 signatures varies considerably over the domain and for large areas in France and the UK it can range from 20 to more than 500% of the influence of fossil fuel emissions. Our simulations suggest that the resulting gradients in Δ 14 CO 2 are well captured in plant samples, but due to their time-varying uptake of CO 2 , their signature can be different with over 3‰ from the atmospheric samples in some regions. We conclude that the framework presented will be well-suited for the interpretation of actual air and plant 14 CO 2 samples.